Field of the Invention
The invention relates to a method of fabricating a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), and more particularly, to a method of fabricating a power MOSFET.
Description of Related Art
A split-gate power MOSFET can also be referred to as a shielded-gate power MOSFET, and the structure thereof includes two separated gates isolated by an inter-poly-dielectric (IPD) inside a trench MOSFET, and thus the two separated gates has two different potentials. The gate located above is configured to form a channel in the MOSFET, and the gate located below is electrically coupled to a source potential via a metal interconnect for generating two-dimensional charge balance under a blocking operation. In addition, the IPD may contribute to the reduction of excessive gate-drain capacitance (Cgd) in a traditional trench MOSFET, so as to reduce switching loss.
However, since the thermal oxidation method used in the manufacture of the split-gate power MOSFET causes diffusion of dopant ions, the two separated gates cannot be effectively isolated. As a result, a higher potential cannot be tolerated when the split-gate power MOSFET is used in high-voltage applications.